The research objective is to elucidate the molecular basis of the process by which phagocytes recognize particulate objects. Ingestion of foreign objects provides the primary defense of hosts against pyogenic infection, and is most efficient when particles possess surface opsonins, particularly IgG and C3. The following specific projects will be pursued in an attempt to elucidate the sensory aspects of this process. 1. Plasma membranes will be isolated from rabbit alveolar macrophages. 2. The effects of several non-ionic detergents upon the electrophoretic patterns of membrane protein and glyco-proteins will be examined on polyacrylamide gels. 3. Agarose gel affinity chromatographic columns will be prepared with opsonic C3 and immunoglobin G. 4. The molecular form of C3 bound to dextran columns will be determined by polyacrylamide gel electrphoresis of components remaining following dextranase treatment of the columns. Binding of opsonins to agarose columns will be quantitated using radiolabelled C3. 5. The interaction of the isolated membranes and the immobilized opsonins will be investigated utilizing affinity chromatography. 6. The functional characteristics of the opsonic recognition molecules eluted from affinity columns will be investigated, and their ability to rebind to opsonins quantitated. The long-term goal of this work is the definition of these interactions in a human system, and the identification of cogenital and acquired abnormalities of opsonic recognition by phagocytes.